This invention relates generally to the automation of semiconductor fabrication operations.
A semiconductor fabrication facility generally includes a large number of different process areas. Each process area may include a specific tool type that is responsible for a particular operation. There may be multiple tool instances of a given tool type. Examples of such process areas include implantation, deposition, etching, metallization, etc.
Wafer lots to be processed pass through the various process areas on their way to becoming completed semiconductor integrated circuit wafers. Thus, a number of steps are done in various process areas, but some alteration of the order of the steps may be possible. In addition, a number of different tools in any process area may be selected to run any particular lot. A lot is a collection of wafers that are grouped together for processing and transport. In other words, any specific process area may have more than one tool that may be capable of performing an operation that a given lot needs.
Generally, the assignment of lots to tools begins with a human operator who manages a given entity cluster. An entity is a semiconductor metrology tool capable of processing a lot. A cluster is a collection of like entities. The operator may notice that lots have arrived or that entities are waiting for lots. The operator may then use heuristics to assign lots to entities. The operator may also use his or her experience to select entities to run lots.
A state-independent constraint is one that is independent of the state of a tool, depending only on the configuration of the tool. The state is a set of variables that define a system such that, knowing the value of the state variables at time zero, one knowing the inputs or system changes can compute the state of the system at a later time. Conversely, a state-dependent constraint is one that depends on what the current state of the tool is, such as what types of lots are running on the tool or how the tool is currently operating.
The operator applies any available constraints, including state-independent and state-dependent constraints, to the lot entity assignments. If any of the constraints are violated, an error may be returned to the human operator. If not, the generated assignments are used to process the lots on entities either manually or automatically.
Ultimately, current management techniques for semiconductor fabrication facilities make relatively limited judgments about optimization, resulting in, to some degree, longer processing times.